Optical network system, optical node device, and optical network control method

ABSTRACT

If wavelength defragmentation is performed during the operation of an optical network, an instantaneous interruption of a network arises; consequently, data are lost; therefore, an optical network control method according to an exemplary aspect of the present invention includes monitoring a data volume of a client signal to be transmitted using a plurality of optical subcarriers; and performing synchronously, depending on a variation in the data volume, an optical subcarrier changing process of changing an active optical subcarrier, of the plurality of optical subcarriers, to be used for transmitting the client signal, and a remapping process of remapping the client signal onto an active optical subcarrier after having been changed.

REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 17/519,717 filed on Nov. 5, 2021, which is acontinuation application of U.S. patent application Ser. No. 16/903,691filed on Jun. 17, 2020, which issued as U.S. Pat. No. 11,201,668, whichis a continuation application of U.S. patent application Ser. No.15/559,899 filed on Sep. 20, 2017, which is issued as U.S. Pat. No.10,715,249, which is a National Stage Entry of PCT/JP2016/001587 filedon Mar. 18, 2016, which claims priority from Japanese Patent Application2015-065717 filed on Mar. 27, 2015, the contents of all of which areincorporated herein by reference, in their entirety.

TECHNICAL FIELD

The present invention relates to optical network systems, optical nodedevices, and optical network control methods and, in particular, to anoptical network system, an optical node device, and an optical networkcontrol method that use the multicarrier transmission scheme.

BACKGROUND ART

Because of a rapid increase in video content services typified by videostreaming services in addition to a rapid spread of advanced terminalsand the like, the transmission capacity in networks is drasticallyincreasing.

Against such a background, it is studied nowadays to introduce amulti-layer network composed of a plurality of layers to communicationcarrier networks. An example of the multi-layer network is aconfiguration in which a packet network in an upper layer is combinedwith an optical network in a lower layer. Here, among adjacent layershierarchized as service networks, a network located at a relativelyupper level is referred to as an upper layer, and a network located at arelatively lower level is referred to as a lower layer.

The upper-layer network is a network configured by using the Internetprotocol (IP) or the multi-protocol label switching (MPLS) technologies,for example. The IP network is characterized by efficient use of networkresources due to the statistical multiplexing effect. In contrast, theoptical network of the lower-layer network is suitable for long-haulhigh-capacity transmission. In general, the network is controlledindependently with respect to each layer. However, it is expected tomaximize efficiency in the use of the network resources and reduceoperational costs by integrating these two types of network layers andcontrolling the network efficiently in response to the traffic demand.

In order to meet a growing traffic demand, it is being studied, inaddition to the introduction of the multi-layer network mentioned above,to introduce new optical network concepts and network operationalmethods. Such examples include elastic network technologies and dynamicnetwork operational technologies.

In the optical network of the lower-layer, the elastic networktechnology is introduced increasingly by which the network can beutilized more flexibly. The elastic network technology is a technologythat enables the transmission with minimum frequency band for thetransmission distance and the transmission throughput by making variablethe modulation scheme in the optical layer, which was fixedconventionally. This makes it possible to maximize the usage efficiencyof optical network resources such as wavelength resources in an opticalfiber. The greatest characteristic of the elastic network technology isthat the transmission granularity in the optical layer can be improvedby introducing the concept of frequency slot with fine granularity of12.5 GHz instead of the conventional fixed grid such as 100 GHz and 50GHz. Hence, it is thought that a multicarrier transmission scheme becomemainstream in the future which transmits signals through a plurality ofphysical media such as a plurality of optical carriers in the opticallayer.

With regard to the network operational technology, it is expected tooperate the network dynamically in contrast to the conventional fixednetwork operation. This is accounted for by the increase in a variationof the traffic of a client to be accommodated in networks. It isexpected that the dynamic operation of optical networks can improve thenetwork usage efficiency.

However, it is pointed out that the introduction of the above-mentionedelastic network technology and dynamic network operational technologycauses a fragment of wavelength bands to arise. This produces theproblem that a path with a long-haul route cannot be secured in the samewavelength due to the occurrence of wavelength fragmentation even thoughthe introduction of the elastic network technology enables theaccommodation efficiency of the entire network to improve. Thefragmentation means a state in which unused wavelength regions arefragmentated in the wavelength usage situation of each link constitutingan optical network. Technologies to resolve the wavelength fragmentationinclude a wavelength defragmentation technology. In general, thewavelength defragmentation technology is a technology to improve theefficiency in the wavelength usage by relocating one wavelengthoccupying a particular link in an optical network to the otherwavelength.

Patent Literature 1 discloses an example of such wavelengthdefragmentation technologies. A related frequency assignment apparatusdescribed in Patent Literature 1 selects a frequency and a routeconnecting a start point and an end point of an optical signal andincludes a route/frequency calculation result storage means, a commonfree frequency information generation means, a free frequency stateevaluation means, and a frequency and route determination means.

The route/frequency calculation result storage means stores route andfrequency calculation results. The common free frequency informationgeneration means extracts fibers connected to each other, and performslogical operation for logical information representing free frequencystates of each of the extracted fibers so as to generate logicalinformation on free frequency states common to fibers. The freefrequency state evaluation means provides an evaluation value for thefree frequency states based on the generated free frequency informationcommon to fibers, in consideration of consecutiveness of freefrequencies in the free frequency state common to fibers. The frequencyand route determination means determines a frequency and passing fibersto be set as a communication route using the evaluation value calculatedin the free frequency state evaluation means as a criterion, and storesthe frequency and the passing fibers in the route/frequency calculationresult storage means.

It is said that the configuration, according to the frequency assignmentapparatus described in Patent Literature 1, makes it possible toeffectively suppress occurrence of fragmentation in a transparent typeoptical path network, and to optimize utilization efficiency ofwavelength (frequency) resources.

Related technologies are described in Patent Literature 2 to PatentLiterature 4.

CITATION LIST Patent Literature

[PTL 1] WO 2012/057095

[PTL 2] WO 2010/032844

[PTL 3] Japanese Unexamined Patent Application Publication (Translationof PCT Application) No. 2006-513672

[PTL 4] Japanese Unexamined Patent Application Publication No.2006-060571

SUMMARY OF INVENTION Technical Problem

The above-mentioned related frequency assignment apparatus receives atraffic transfer demand, determines a route on a network, and assigns awavelength along the determined route. That is to say, the apparatusassigns a frequency so as to suppress the occurrence of fragmentation ininitializing the network setting.

However, if such frequency assignment is performed during networkoperation, an instantaneous interruption of the network arises, whichcauses the problem that data are lost.

As mentioned above, there has been the problem that an instantaneousinterruption of a network arises; consequently, data are lost, ifwavelength defragmentation is performed during the operation of anoptical network.

The object of the present invention is to provide an optical networksystem, an optical node device, and an optical network control methodthat solve the above-mentioned problem that an instantaneousinterruption of a network arises; consequently, data are lost, ifwavelength defragmentation is performed during the operation of anoptical network.

Solution to Problem

An optical network control method according to an exemplary aspect ofthe present invention includes monitoring a data volume of a clientsignal to be transmitted using a plurality of optical subcarriers; andperforming synchronously, depending on a variation in the data volume,an optical subcarrier changing process of changing an active opticalsubcarrier, of the plurality of optical subcarriers, to be used fortransmitting the client signal, and a remapping process of remapping theclient signal onto an active optical subcarrier after having beenchanged.

An optical network system according to an exemplary aspect of thepresent invention includes a plurality of optical node devices; and anetwork management device configured to have centralized control overthe plurality of optical node devices, wherein the optical node deviceincludes a client-side interface means for accommodating a client signalto be transmitted using a plurality of optical subcarriers, across-connect means, a line-side interface means for generating theplurality of optical subcarriers, and a control means for communicatingwith the network management device, and the cross-connect means includesa client signal monitoring means for monitoring a data volume of theclient signal, and synchronously performs, depending on a variation inthe data volume, an optical subcarrier changing process of changing anactive optical subcarrier, out of the plurality of optical subcarriers,to be used for transmitting the client signal, and a remapping processof remapping the client signal onto an active optical subcarrier afterhaving been changed.

An optical node device according to an exemplary aspect of the presentinvention includes a client-side interface means for accommodating aclient signal to be transmitted using a plurality of opticalsubcarriers; a cross-connect means; a line-side interface means forgenerating the plurality of optical subcarriers; and a control means forcommunicating with the network management device, wherein thecross-connect means includes a client signal monitoring means formonitoring a data volume of the client signal, and synchronouslyperforms, depending on a variation in the data volume, an opticalsubcarrier changing process of changing an active optical subcarrier,out of the plurality of optical subcarriers, to be used for transmittingthe client signal, and a remapping process of remapping the clientsignal onto an active optical subcarrier after having been changed.

Advantageous Effects of Invention

According to an optical network system, an optical node device, and anoptical network control method of the present invention, it is possibleto perform wavelength defragmentation without data loss due to aninstantaneous interruption of a network even when an optical network isoperating.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a diagram illustrating active optical subcarriers in eachlink to explain an optical network control method according to a firstexample embodiment of the present invention.

FIG. 1B is a diagram illustrating time variation in the active opticalsubcarrier and the throughput of a client signal to explain the opticalnetwork control method according to the first example embodiment of thepresent invention.

FIG. 2 is a block diagram schematically illustrating the configurationof an optical network system according to the first example embodimentof the present invention.

FIG. 3 is a block diagram illustrating the configuration of an opticalnode device constituting the optical network system according to thefirst example embodiment of the present invention.

FIG. 4 is a diagram illustrating a network topology to explain theoperation of the optical network system according to the first exampleembodiment of the present invention.

FIG. 5A is a diagram illustrating a wavelength usage situation beforeperforming wavelength defragmentation in the optical network systemaccording to the first example embodiment of the present invention.

FIG. 5B is a diagram illustrating a wavelength usage situation afterperforming wavelength defragmentation in the optical network systemaccording to the first example embodiment of the present invention.

FIG. 6 is a flowchart to explain the operation of a network managementdevice included in the optical network system according to the firstexample embodiment of the present invention.

FIG. 7A is a diagram illustrating a wavelength usage situation before astop of the operation of an optical subcarrier in the optical networksystem according to a second example embodiment of the presentinvention.

FIG. 7B is a diagram illustrating a wavelength usage situation after astop of the operation p of the optical subcarrier in the optical networksystem according to the second example embodiment of the presentinvention.

FIG. 7C is a diagram illustrating a wavelength usage situation afterreactivating the optical subcarrier in the optical network systemaccording to the second example embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Example embodiments of the present invention will be described belowwith reference to the drawings.

First Example Embodiment

An optical network control method according to the present exampleembodiment will be described. In the optical network control methodaccording to the present example embodiment, first, a data volume of aclient signal to be transmitted using a plurality of optical subcarriersis monitored. An optical subcarrier changing process and a remappingprocess are synchronously performed depending on a variation in the datavolume. The optical subcarrier changing process is a process of changingan active optical subcarrier, of a plurality of optical subcarriers, tobe used for transmitting the client signal. The remapping process is aprocess of remapping the client signal onto an active optical subcarrierafter having been changed.

Next, the optical network control method according to the presentexample embodiment will be described specifically with reference to FIG.1A and FIG. 1B. FIG. 1A is a diagram illustrating active opticalsubcarriers in each link, and FIG. 1B is a diagram illustrating timevariation in the active optical subcarrier and the throughput of aclient signal.

In the initial state, the link between node A and node B is operated byan optical multicarrier having four kinds of optical subcarrierwavelengths (λ1, λ2, λ3, λ4). In the link between node B and node C,another service is provided by using optical subcarriers havingwavelengths λ5 and λ6. In such an initial wavelength usage situation, itis impossible to provide newly end-to-end service from node A to node C.

However, it is configured in the optical network control method of thepresent example embodiment to perform wavelength defragmentation bysynchronously performing the optical subcarrier changing process and theremapping process depending on a variation in the data volume of aclient signal. Consequently, according to the optical network controlmethod of the present example embodiment, it is possible to perform thewavelength defragmentation without data loss due to an instantaneousinterruption of a network even when an optical network is operating.This enables the above-mentioned new service to be provided.

A more specific description will be given using the example illustratedin FIG. 1B. The above-mentioned variation in the data volume(throughput) will be described using as an example a case where the datavolume decreases with the decrement of the data volume varying in excessof the transmission capacity of a single optical subcarrier. That is tosay, as illustrated in FIG. 1B, it will be assumed that the clientcommunication demand decreases by an optical subcarrier when an opticalnetwork is operating. Then, the client data are mapped and aggregatedinto three optical subcarriers having the wavelengths λ1, λ2, and λ3,and the setting of the wavelength of the optical subcarrier having thewavelength λ4 is changed into the wavelength λ6 in preparation forresumption of operation. This enables the wavelength defragmentation tobe performed when the optical network is operating.

As a result, as illustrated in FIG. 1A, it becomes possible to use anend-to-end link from node A to node C with the wavelength λ4 byrelocating the optical subcarrier having the wavelength λ4 to theoptical subcarrier having the wavelength λ6.

Next, an optical network system according to the present exampleembodiment will be described. FIG. 2 is a block diagram schematicallyillustrating the configuration of an optical network system according tothe present example embodiment. FIG. 3 is a block diagram illustratingthe configuration of an optical node device constituting the opticalnetwork system according to the present example embodiment.

An optical network system 1000 according to the present exampleembodiment includes a network management device 100 and a plurality ofoptical node devices 200. The network management device 100 has thefunction of having centralized control over the plurality of opticalnode devices 200 and is implemented in a network management system(NMS), for example. As illustrated in FIG. 2 , each optical node device200 serves as a node device in which multiple layers including anoptical layer and an IP layer are integrated.

As illustrated in FIG. 3 , the optical node device 200 includes aclient-side interface 210 configured to connect to a client-side network300, a cross-connect section 220, a line-side interface 230 configuredto connect to a backbone network 400, and a controller 240.

The client-side interface 210 accommodates a client signal to betransmitted using a plurality of optical subcarriers. The line-sideinterface 230 generates a plurality of optical subcarriers. Thecontroller 240 has the function of communicating with the networkmanagement device 100.

The cross-connect section 220 includes a client signal monitor 222configured to monitor the data volume of a client signal. An opticalsubcarrier changing process and a remapping process are synchronouslyperformed depending on a variation in the data volume. The opticalsubcarrier changing process is a process of changing an active opticalsubcarrier, of a plurality of optical subcarriers, to be used fortransmitting a client signal. The remapping process is a process ofremapping the client signal onto an active optical subcarrier afterhaving been changed.

The configuration of the optical node device 200 will be described inmore detail subsequently.

The client-side interface 210 is capable of accommodating client datawith various granularities from layer one to layer three in the OSI(open systems interconnection) reference model.

The cross-connect section 220 can perform aggregation control andfragmentation control in addition to switching control of client data tobe transferred.

The client signal monitor 222 detects the data volume such as framevolume and packet volume with respect to each transfer service of aclient. The client signal monitor 222 can be configured to notify thecontroller 240 of the variation in the data volume. The variation in thedata volume includes a case where the data volume decreases with thedecrement of the data volume varying in excess of the transmissioncapacity of a single optical subcarrier. More specifically, for example,when the client signal monitor 222 detects the data volume above a setthreshold level, the client signal monitor 222 can notify the controller240 of that effect, and the controller 240 can send it to the networkmanagement device 100. The threshold level is set typically on the basisof a throughput that can be mapped onto a single optical subcarrier.

The line-side interface 230 has the function of generating a pluralityof optical subcarriers and forming a multicarrier.

Next, the operation of the optical network system 1000 and the opticalnetwork control method according to the present example embodiment willbe described in more detail.

The case will be described below as an example where an optical networksystem has a network topology including four optical node devices withtandem connection, as illustrated in FIG. 4 . The optical layer will bedescribed using as an example a communication system where a maximum offour optical subcarriers are used each of which has a throughput of 100Gbps, that is, the transmission is performed up to 400 Gbps.

FIG. 5A and FIG. 5B illustrate wavelength usage situations at aspecified time in the optical network system 1000. FIG. 5A illustratesthe wavelength usage situation before wavelength defragmentation, andFIG. 5B illustrates the wavelength usage situation after wavelengthdefragmentation. In FIG. 5A and FIG. 5B, the horizontal axes represent alink in which respective optical node devices included in node A to nodeD are connected in series, and the vertical axes represent operatingwavelengths in each link.

As illustrated in FIG. 5A, the wavelength usage situation beforewavelength defragmentation is brought to a situation where unusedwavelength regions are finely fragmentated due to repetitions of serviceoperation and stop. In the case illustrated in FIG. 5A, for example,service 1 is operated in the link from node A to node B using amulticarrier including three optical subcarriers having the wavelengthsλ8, λ9, and λ10. That is to say, in the wavelength usage situationillustrated in FIG. 5A, end-to-end service from node A to node D cannotbe provided.

Next, the operation of the network management device 100 constitutingthe optical network system 1000 will be described. FIG. 6 is a flowchartto explain the operation of the network management device 100.

The network management device 100 performs a process of minimizing astate in which unused optical subcarriers are fragmentated, that is, awavelength defragmentation process.

As illustrated in FIG. 6 , the operation (control algorithm) of thenetwork management device 100 is divided into three parts. The firstpart is an algorithm to determine path processing sequence (step S100).The second part is an algorithm to select an optical subcarrier whoseoperation to be stopped included in an active optical multicarrierdepending on the traffic volume of client data. That is to say, thesecond part is a process of selecting a change candidate opticalsubcarrier whose operation to be stopped from among active opticalsubcarriers (step S200). The third part is an algorithm to newlyreconfigure the wavelength of the optical subcarrier whose operation hasbeen stopped for resumption of operation. That is to say, the third partis a process of setting the wavelength of a changed optical subcarrierthat becomes an active optical subcarrier due to the change (step S300).

First, a database of optical paths to become candidates for wavelengthdefragmentation, that is, a database of services, is generated (stepS10). The condition of the optical path to become a candidate is thatthe optical path is composed of a multicarrier and has unused slots inadjacent links. It is detected that the traffic volume of a clientsignal exceeds a threshold value, which serves as a trigger and gets itstarted to extract an optical subcarrier on which wavelengthdefragmentation is going to be performed.

In the example illustrated in FIG. 5A, four types of services from serve1 to serve 4 are targeted for wavelength defragmentation and stored inthe database. Service 5 is also provided by the multicarriertransmission using two wavelengths; however, the service is not targetedbecause the adjacent links are already occupied and include no unusedslots.

When the throughput of the client signal decreases, and the decrementexceeds the throughput of the single optical subcarrier, the opticalnode device 200 sends out a trigger signal to the network managementdevice 100. That is to say, the time when it is determined that thetransfer capability of the optical layer becomes excessive is set at thestart time of the wavelength defragmentation process.

The network management device 100 first executes an algorithm todetermine the processing sequence of the optical path (step S100). Inthis case, the process is started in ascending order of the number oflinks with respect to the optical paths registered in the database (stepS110). If the number of links of the optical path is the same, theprocess is started with respect to the optical paths in descending orderof the number of active subcarriers (step S120). If the number ofsubcarriers is also the same, the process is performed with respect tothe optical paths in ascending order of the wavelength (step S130). Inaddition, if the wavelength is the same, the process is performed withrespect to the optical paths in ascending order of distance from theoptical node device with a lower-degree node number (step S140). It iscompleted by the above processes to determine an optical path to betargeted for the wavelength defragmentation that is preferentiallyprocessed (step S150).

Next, optical subcarriers are selected in descending order of the numberof consecutive unused slots in adjacent links in the same wavelengthslot from a plurality of optical subcarriers constituting the opticalpath that has been determined to be processed. That is to say, anoptical subcarrier with a maximum number of consecutive unused opticalsubcarriers in adjacent links in the same wavelength band is selected asa change candidate optical subcarrier from the plurality of opticalsubcarriers (step S210).

If the number of unused slots is the same, optical subcarriers areselected in descending order of the number of unused optical subcarriersin adjacent wavelength slots. That is to say, an optical subcarrier witha maximum number of unused optical subcarriers is selected as a changecandidate optical subcarrier from optical subcarriers in adjacentwavelength bands (step S220). This is because an optical path having awide wavelength slot width and capable of long-haul transmission can besecured by relocating an optical subcarrier having a large number ofadjacent unused wavelength slots. The number of wavelength slots is setat the total number of wavelength slots between transmitting andreceiving nodes. If the number of unused wavelength slots is also thesame, the process is performed in ascending order of wavelength (stepS230).

By performing the above processes, an optical subcarrier whose operationwill be stopped is determined (step S240). Even if threshold detectiontriggers to stop the operation of two optical subcarriers aresimultaneously obtained, the processes can be performed by using asimilar algorithm to the above-mentioned algorithm.

Next, an algorithm to reconfigure the wavelength of the opticalsubcarrier whose operation has been stopped for resumption of operationis executed. That is to say, the process of setting the wavelength of achanged optical subcarrier is performed (step S300).

Even in this case, as with the above-mentioned algorithm to select anoptical subcarrier whose operation will be stopped, the process isstarted in ascending order of path distance, that is, from an activeoptical subcarrier with the minimum number of links (step S310).

First, set wavelengths are selected with respect to the wavelength slotin descending order of usage rate of links adjacent to the target link.That is to say, the wavelength of the changed optical subcarrier is setat the wavelength of an optical subcarrier with the maximum number ofoptical subcarriers in use in adjacent links in the same wavelength band(step S320).

If the number of optical subcarriers in use in adjacent links is thesame, set wavelengths are selected in descending order of the number ofadjacent wavelength slots in use. That is to say, the wavelength of thechanged optical subcarrier is set at the wavelength of an opticalsubcarrier with the maximum number of optical subcarriers in use out ofoptical subcarriers in adjacent wavelength bands (step S330). Thisprocess is similar to the Most-used algorithm, which is a commonalgorithm to set a wavelength. If the number of optical subcarriers inuse in adjacent wavelength bands is the same, the selection is performedin ascending order of wavelength (step S340).

By executing the above-mentioned algorithm, the wavelength of an opticalsubcarrier to be operated again is determined (step S350).

After that, the operation of the optical subcarrier is stopped, and thedatabase is updated. Then the next optical path is processed (step S20).When a threshold detection trigger for the traffic volume of the clientis detected, the operation is started using an optical subcarrier havinga new wavelength (step S30), and the wavelength defragmentation processis completed.

The above-mentioned algorithm of wavelength defragmentation according tothe present example embodiment will be specifically described below withreference to the wavelength usage situation illustrated in FIG. 5A.

In the wavelength usage situation before wavelength defragmentationillustrated in FIG. 5A, it is determined that five services from service1 to service 5 are targeted for wavelength defragmentation control, andthey are stored in the database. The case will be described below wherea decrease in the throughput of the client signal is detected in each ofthe five services. The amount of decrease in throughput corresponds tothe transmission capacity per optical subcarrier in each service. Thatis to say, each service uses more optical subcarriers in the opticallayer than specifications by one optical subcarrier.

First, the sequence of the processes of the five services is determined.As mentioned above, services ranging between a small number of links arepreferentially processed. Service 1 ranges from node A to node B,service 2 ranges from node C to node D, and the number of links is onein each service; consequently, these services are processed in priorityto other services. If the number of links is the same, the process isperformed in descending order of the number of optical subcarriers.Service 1 uses three optical subcarriers with the wavelengths λ8, λ9,and λ10, and service 2 uses two optical subcarriers with the wavelengthsλ1 and λ2. Accordingly, the wavelength defragmentation process ispreferentially performed on service 1 that uses a larger number ofoptical subcarriers.

Next, an optical subcarrier whose operation will be stopped is selectedfrom among the optical subcarriers constituting service 1. As mentionedabove, service 1 uses three optical subcarriers with the wavelengths λ8,λ9, and λ10. Optical subcarriers are selected from among these threeoptical subcarriers in descending order of the number of consecutiveunused slots in adjacent links in the same wavelength slot. With regardto the optical subcarriers with the wavelengths λ9 and λ10, the numberof adjacent unused slots is equal to zero because service 5 has alreadybeen operated in the adjacent link ranging from node B to node D. Incontrast, with regard to the optical subcarrier with the wavelength λ8,the number of adjacent unused slots is equal to two because there is noservice operated in the adjacent link ranging from node B to node D. Asa result, it is determined that the optical subcarrier with thewavelength λ8 in the optical subcarriers constituting service 1 is anoptical subcarrier whose operation will be stopped (change candidateoptical subcarrier).

Next, a wavelength used in resumption of operation will be set. Asrelocation candidates for the optical subcarrier with the wavelength λ8constituting service 1, there are three wavelength slots with λ1, λ3,and λ6. First, set wavelengths are selected from among these threewavelengths in descending order of usage rate of wavelength slot inlinks adjacent to the target link. That is to say, the usage rate withregard to the wavelengths λ1 and λ3 is equal to zero because theadjacent links are unused, and the usage rate with regard to thewavelength λ6 is equal to one because service 4 is operated in theadjacent link ranging from node B to node D. Hence, the wavelength λ6,at which the usage rate in adjacent links is higher, is set at awavelength to be reconfigured.

With regard to service 2 to be targeted for the wavelengthdefragmentation control subsequently to service 1, the process is alsoperformed using a similar algorithm. In service 2, the opticalsubcarrier with the wavelength λ1 is targeted for the wavelengthdefragmentation by an algorithm similar to that for service 1. Thewavelengths of relocation candidates at the resumption of operation arenarrowed down to λ4 and λ5 from λ4, λ5, and λ8 to be candidates based onthe usage rate of the adjacent link. Because the usage rate of theadjacent wavelength is also the same with regard to both thesewavelengths, the shorter wavelength λ4 is selected as a relocationdestination.

With regard to service 3 and service 4, the process is performed inascending order of wavelength because the number of links and the numberof optical subcarriers are the same. In this case, service 3 becomes anext target to be processed. Service 3 is operated using two opticalsubcarriers having the wavelengths λ4 and λ5. The optical subcarrierhaving the wavelength λ1 operated in service 2 is relocated to theadjacent link with the wavelength λ4 between node C and node D.Comparing the number of adjacent unused wavelength slots, it becomesequal to zero for λ4 and one for λ5; consequently, the opticalsubcarrier having the wavelength λ5 becomes an optical subcarrier whoseoperation will be stopped. With regard to service 4, the opticalsubcarrier having the wavelength λ6 is a target to be processed;however, it does not become a candidate for the wavelengthdefragmentation because it reaches a state ex-post facto in which thereis no unused wavelength slot in adjacent links.

By the wavelength defragmentation process using the above-mentionedalgorithm, the wavelength usage situation after the wavelengthdefragmentation reaches the state illustrated in FIG. 5B. The wavelengthusage situations before the wavelength defragmentation (FIG. 5A) andafter the wavelength defragmentation (FIG. 5B) will be compared below.Although there is no consecutive wavelength bands from node A to node Dbefore the wavelength defragmentation, it becomes possible to secureconsecutive wavelength bands in three wavelength bands of thewavelengths λ1, λ5, and λ8 after the wavelength defragmentation.

Next, a band control technology according to the present exampleembodiment will be described.

As mentioned above, depending on the wavelength usage situation managedby the network management device 100, a particular optical subcarrierincluded in a multicarrier is selected as a target for the wavelengthdefragmentation. Therefore, it is necessary as the band controltechnology to change the number of optical subcarriers and correspondingmapping table of client data.

That is to say, the optical node device 200 performs an opticalsubcarrier changing process based on the results of the process ofselecting a change candidate optical subcarrier and the process ofsetting the wavelength of a changed optical subcarrier, and performs aremapping process as well. The remapping process includes a process ofremapping a client signal onto an optical subcarrier other than a changecandidate optical subcarrier out of a plurality of optical subcarriers.

In the present example embodiment, a band control technologyuninterruptedly using the synchronization technology for transmissionframes is employed. In order to change the number of optical subcarriersuninterruptedly, it is necessary to dynamically change the framesynchronization condition of optical subcarriers to be transmittedthrough a plurality of lanes and the condition for mapping client dataonto an optical subcarrier. The synchronization condition oftransmission frames in a plurality of lanes can be achieved by extendingthe LCAS (link capacity adjustment scheme) technology in SDH(synchronous digital hierarchy) transmission to the OTN (opticaltransport network). The LCAS is a technology designed to increase anddecrease the bandwidth of layer 1 configured by the GFP (generic framingprocedure) or VCAT (virtual concatenation) uninterruptedly. That is tosay, the LCAS technology is a technology designed to change the numberof transmission lanes uninterruptedly by switching between lanessynchronously between a transmitting node and a receiving node.

The condition for mapping client data onto an optical subcarrier isachieved by updating a transfer table of data held in the cross-connectsection in conjunction with the above-mentioned frame synchronization.This makes it possible to change the mapping condition uninterruptedly.

The case will be described where the MAC (media access control) frame inlayer 2 is accommodated in the OTU frame of layer 1 and transmitted. Ifthe maximum throughput of layer 2 data is larger than the throughput ofa single optical subcarrier, the transmission frame of client data isdivided into a plurality of processing lanes by the fragmentationprocess of MAC frame and then mapped onto a plurality of opticalsubcarriers. If the client data volume decreases, the cross-connectsection 220 in the optical node device 200 changes a processing tablefor the fragmentation process in order to decrease the number of outputlanes. Concurrently with the change in the processing table, lane changeinformation is sent to a counter node, and the number of lanes isswitched simultaneously between the transmitting node and the receivingnode. This makes it possible to change the number of lanesuninterruptedly.

In this manner, the optical node device 200 according to the presentexample embodiment performs an optical subcarrier changing process and aremapping process synchronously. The optical subcarrier changing processis a process of switching transmission lanes to transmit opticalsubcarriers synchronously between a transmitting side and a receivingside. The remapping process is a process of updating the transfer tableof client signals synchronously between the transmitting side and thereceiving side.

At the resumption of operation, likewise, change information on thenumber of lanes is sent to the counter node using an increase in theclient signal as a trigger signal, and the number of lanes is switchedsimultaneously between the transmitting side and the receiving side. Atthe same time, the cross-connect section in each of the transmitting andreceiving nodes performs a process of changing the processing table.

That is to say, a case where the data volume decreases and thenincreases is regarded as the variation in data volume. In this case, theoptical subcarrier changing process is a process of adding a changedoptical subcarrier to an active optical subcarrier. The remappingprocess is a process of remapping a client signal onto the changedoptical subcarrier and an optical subcarrier other than a changecandidate optical subcarrier of a plurality of optical subcarriers.

As mentioned above, according to the optical network system, the opticalnode device, and the optical network control method of the presentexample embodiment, it is possible to perform wavelength defragmentationwithout data loss due to an instantaneous interruption of a network evenwhen an optical network is operating.

Second Example Embodiment

Next, a second example embodiment of the present invention will bedescribed. The second example embodiment differs from the first exampleembodiment in an accommodation form of a client signal. Although thecase is described in the first example embodiment where a single type ofclient signal is processed, a case will be described in the presentexample embodiment where the client signal includes many different typesof client signals. That is to say, a case will be described where aplurality of client services are accommodated with the same destinationin the communication between the same transmitting node device and thesame receiving node device. Because the configurations of an opticalnetwork system and an optical node device, and a control algorithm inthe present example embodiment are the same as those in the firstexample embodiment, their descriptions are not repeated.

The case will be described in the present example embodiment where theclient signals are a plurality of client data such as an LSP (labelswitched path) in the MPLS-TP (multi-protocol label switching—transportprofile). The plurality of client data as described above are mappedonto a plurality of optical subcarriers and transmitted with the samedestination, as is the case with the first example embodiment.

If the throughput of particular client data such as an LSP in theMPLS-TP out of a plurality of client data decreases, the particularclient data are relocated and mapped onto an optical subcarrier ontowhich other client data (LSP) have been already mapped. Then theoperation of the optical subcarrier is stopped that becomes unused afterthe client data is relocated.

A more detailed description will be given below with reference to FIG.7A, FIG. 7B, and FIG. 7C.

FIG. 7A illustrates a configuration example in which a plurality of LSPsare mapped onto a plurality of optical subcarriers. As illustrated inFIG. 7A, the case will be described as an example where five types ofclient data (LSP-1 to LSP-5) are mapped onto four optical subcarrierseach of which has a throughput of 100 Gbps. In this case, the five typesof data from LSP-1 to LSP-5 are accommodated in a virtual container ofODU4-4v (optical channel data unit).

When the client capacity of the client data from LSP-1 to LSP-5 fallsbelow 300 Gbps or less, for example, the data volume of LSP-2 (2) andLSP-4 (4) decreases, LSP-2 (2) is relocated to an optical subcarrier forLSP-4 (4), as illustrated in FIG. 7B. In addition, the most appropriateoptical subcarrier for resolution of wavelength defragmentation, thatis, an optical subcarrier DF serving as a wavelength defragmentationcandidate is selected based on the wavelength usage situation that ismanaged in the network management device (NMS). Then the client datamounted in the optical subcarrier DF, that is, the client data (5) ofLSP-5 in the example illustrated in FIG. 7A, is relocated to the opticalsubcarrier onto which LSP-2 has been mapped. At the same time, theoperation of the optical subcarrier DF is stopped, and the client dataare accommodated in ODU4-3v with the number of frame concatenationsdecremented by one. It is possible to perform the above band controluninterruptedly, as is the case with the first example embodiment.

After that, the resumption of operation process is performed using anincrease in the number of client signals as a trigger signal. In thiscase, as a result of the wavelength defragmentation, the client data (5)of LSP-5 are relocated to an optical subcarrier whose wavelength slotdiffers from that of the optical subcarrier DF, as illustrated in FIG.7C.

Even in the resumption of operation process, as is the case withdecreasing the number of lanes, the use of the LCAS technology makes itpossible to notify a counter node of the change information on thenumber of lanes (an increase in the number of lanes) and increase thenumber of lanes uninterruptedly synchronously between the transmittingnode and the receiving node. The cross-connect section included in theoptical node device at each node performs the process of changing theprocessing table to switch the LSPs in synchronization with the changein the number of lanes.

As mentioned above, according to the optical network system, the opticalnode device, and the optical network control method of the presentexample embodiment, it is possible to perform wavelength defragmentationwithout data loss due to an instantaneous interruption of a network evenwhen an optical network is operating.

Third Example Embodiment

Next, a third example embodiment of the present invention will bedescribed. An optical node device according to the third exampleembodiment differs from the optical node device 200 according to thefirst example embodiment in that a traffic prediction section isincluded. Because other configurations are the same as those in thefirst example embodiment, their descriptions are not repeated.

In the optical node device according to the present example embodiment,a cross-connect section starts performing a process when the trafficprediction section predicts the data volume of a client signal to varyin excess of the transmission capacity of a single optical subcarrier.The traffic prediction section can include a data holding section and adata analysis section. The data holding section holds a traffic volumethat is detected at specified time intervals. The data analysis sectiondetects a gradient of a traffic variation. The traffic predictionsection is disposed in the client-side interface 210 or thecross-connect section 220.

It is configured in the first and second example embodiments that atrigger signal is given off when the decrement of the throughput of theclient signal exceeds the throughput of the single optical subcarrier.That is to say, the time when it is determined that the transfercapability of the optical layer becomes excessive is set at the starttime of the wavelength defragmentation process.

In contrast, it is configured in the present example embodiment that thetraffic prediction section estimates a timing from a variation historyof a traffic variation and gives off a trigger signal. The trafficprediction section detects a data volume of a client signal in real timeand predicts a client data volume after a certain period of time by agradient of an increase or decrease in the variation. This enables thecross-connect section 220 to secure more time to perform a processrequired for the wavelength defragmentation.

As mentioned above, according to the optical node device and the opticalnetwork system using the same of the present example embodiment, it ispossible to perform wavelength defragmentation without data loss due toan instantaneous interruption of a network even when an optical networkis operating.

The present invention has been described above by taking theabove-described example embodiments as exemplary examples. However, thepresent invention is not limited to the above-described exampleembodiments. In other words, various modes which would be understood bythose skilled in the art are applicable to the present invention withinthe scope of the present invention.

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2015-065717, filed on Mar. 27, 2015, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

1000 . . . optical network system

100 . . . network management device

200 . . . optical node device

210 . . . client-side interface

220 . . . cross-connect section

222 . . . client signal monitor

230 . . . line-side interface

240 . . . controller

300 . . . client-side network

400 . . . core network

1. An optical network management device, comprising: a receiverconfigured to receive a notice of data variation in a client signal on anetwork; and a controller configured to perform a control to decrease afragmentation of unused part of an optical subcarrier on the network,wherein the controller is configured to change, depending on the datavariation having been received, an active optical subcarrier, which isthe optical subcarrier to be used for transmitting the client signal,synchronously between an optical transmitting node and an opticalreceiving node, map the client signal onto the active optical subcarrierhaving been changed, synchronously between the optical transmitting nodeand the optical receiving node, and perform synchronously a changingprocess of the active optical subcarrier and a mapping process of theclient signal.
 2. The optical network management device according toclaim 1, wherein the controller is configured to perform a first controlto select a change candidate optical subcarrier whose operation to bestopped from among the active optical subcarrier, a second control toset a wavelength of a changed optical subcarrier that becomes the activeoptical subcarrier due to a change, and a third control to change theactive optical subcarrier, based on respective results of the firstcontrol and the second control.
 3. The optical network management deviceaccording to claim 2, wherein the controller is configured to perform acontrol to map the client signal onto the optical subcarrier other thanthe change candidate optical subcarrier out of the optical subcarrier.4. The optical network management device according to claim 2, whereinthe controller is configured to start the first control and the secondcontrol from the active optical subcarrier with a minimum number oflinks.
 5. The optical network management device according to claim 2,wherein the controller is configured to select an optical subcarrierwith a maximum number of consecutive unused optical subcarriers in anadjacent link in an identical wavelength band as the change candidateoptical subcarrier from the optical subcarrier.
 6. The optical networkmanagement device according to claim 5, wherein the controller isconfigured to select an optical subcarrier with a maximum number ofunused optical subcarriers as the change candidate optical subcarrierfrom optical subcarriers in an adjacent wavelength band when number ofthe consecutive unused optical subcarriers is equal.
 7. The opticalnetwork management device according to claim 2, wherein the controlleris configured to set a wavelength of the changed optical subcarrier at awavelength of an optical subcarrier with a maximum number of opticalsubcarriers in use in an adjacent link in an identical wavelength band.8. The optical network management device according to claim 3, whereinthe controller is configured to select an optical subcarrier with amaximum number of consecutive unused optical subcarriers in an adjacentlink in an identical wavelength band as the change candidate opticalsubcarrier from the optical subcarrier.
 9. The optical networkmanagement device according to claim 8, wherein the controller isconfigured to select an optical subcarrier with a maximum number ofunused optical subcarriers as the change candidate optical subcarrierfrom optical subcarriers in an adjacent wavelength band when number ofthe consecutive unused optical subcarriers is equal.